Pop the top, take a sip and you'll find a bit more than a mineral or caffeinated beverage.

Sparks and Tilt — affectionately known as "alcopops" — are caffeinated malt beverages that contain as much as twice the alcohol of many beers. It's a combination stimulant and depressant in one that keeps partygoers, well, partying and uninhibited.

Many teens may be in on the secret. But some consumer activists and authorities say the labels fool parents and all too often store clerks who sell them — sometimes unwittingly — to minors.

"We think there is a deliberate attempt to confuse," said Michael Scippa, advocacy director for the Marin Institute, an alcohol industry watchdog organization studying the issue.

They are available at most retail stores, usually stocked with beer. But there is growing support for the Marin Institute's cause.

Last summer, 29 state attorneys general issued a statement that the alcopops threatened the health and safety of America's youth.

In April, the state Department of Business and Professional Regulation concluded a statewide investigation of more than 900 businesses that resulted in 173 arrests of merchants who sold alcoholic energy drinks to teen-aged operatives. The arrests included nine merchants in the Tampa Bay area who sold Sparks and Tilt to minors.

And now the Center for Science in the Public Interest, a consumer advocacy organization in Washington, D.C., is pressuring Miller Brewing and Anheuser-Busch to stop mixing stimulants with alcohol to form what the organization likes to call "alcospeed." Though research is limited, the center believe the drinks raise risks of binges among under-aged consumers and can increase the threat to their health and safety.

Don Murray, executive director of the Florida chapter of Mother's Against Drunk Driving, said he is not challenging any adults' right to consume a legal beverage. But he's troubled by the confusion over the labeling and marketing.

"We need to get more serious about control of our sell points," Murray said.

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Julian Green, a spokesman for Sparks maker Miller Brewing, said there is no attempt to market Sparks to underage drinkers.

"This is not marketed to kids," Green said. "All of our Sparks brands are clearly labeled with alcohol. Alcohol is referenced no fewer than four times."

Sparks' label does clearly state that it contains alcohol. But there still are questions about whether the aim is to market it to minors.Visit the Sparks web site and it reads more like a MySpace page or even a Dora the Explorer cartoon map than a grown-up, alcohol beverage site.

The labeling on a can of Anheuser-Busch's Tilt, the alcohol content is less obvious than on the Sparks can. At the top, it reads "Alc.," instead of "alcohol." And, in tiny print at the bottom, it states that it is 8 percent alcohol by volume.

Anheuser-Busch did not respond to inquiries about Tilt.

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Sparks, Tilt and other canned caffeinated malt beverages emerged from bars where, for years, the energy drink Red Bull has been combined with alcohol.

Among the favorites are RBV or Red Bull with vodka, and the "Jager Bomb," a mix of Red Bull and Jagermeister herbal liqueur.

"It's pretty popular," said Tampa bartender Cathleen Mineo, 23. "The more popular one is the Red Bull with vodka."

Meagan Eckerle, of Brandon, has been drinking the concoction since she was 16.

With the combination energy drink and alcohol, Eckerle, 21, morphed to a bit of a party animal from a "grandma."

"On the dance floor, it keeps me hyped all night," the Hillsborough Community College junior said. "It keeps me going."

Drinking the Red Bull-and-vodka combination led her to try Tilt. But she doesn't like it because "it tastes like orange soda."

Aspiring teacher Steven Godwin, 20, of Tampa, drinks Sparks sometimes, though he prefers a beer. Godwin believes Sparks and Tilt are drinks designed for his peer group.

"How many people over 21 drink Sparks? I don't know anybody," he said. "I know people younger than me who drink it."

There's 18-year-old Tasha Bond, a Brandon resident and University of Tampa student. She also has tried Sparks, because she didn't like the taste of beer.

In Sparks, "you can't taste the alcohol," she said.

In every case of those questioned about their decision to drink the alcohol-energy beverage combination, they all said it was for the same purpose Eckerle said she did it — the mix gives them an ability like no other.

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What exactly does a drink loaded with caffeine and high alcohol volume do to the body?

The studies are few. But Dr. Mary Claire O'Brien is working to figure it out.

O'Brien, a researcher at the Wake Forest University School of Medicine in Winston-Salem, N.C., studying the issues of injuries related to college drinking, says the combination opens consumers to high risks.

First, there's the mixing of a stimulant and depressant.

Then, the caffeine level isn't like an average cup of coffee, O'Brien says.

Sparks lists caffeine as an ingredient. It also lists guarana, which O'Brien describes as another form of natural caffeine, making it at least a double jolt.

The 6 percent alcohol by volume is more than a Bud Light.

O'Brien says the high volume of caffeine temporarily suppresses the effects of the alcohol, enabling a person to drink more than normal without "feeling as drunk." It gives the person energy to party while releasing their inhibitions.

But caffeine metabolizes faster than alcohol, so once the caffeine wears off, the alcohol kicks in. And the drinkers who drank too much crash.

"You can't drink enough rum and Coke to do what these beverages do to you," O'Brien said.

Her study of the effects of alcopops found about a quarter of college students who drink alcoholic beverages mixed them with energy drinks. And she found the effects troubling.

"Students were twice as likely to report riding with a drunken driver; twice as likely to be hurt or injured and to require medical treatment; greatly at risk of being taken advantage of sexually or taking advantage of someone sexually," O'Brien said.

The energy drink-and-alcohol combination was the next step in the increasingly lucrative energy beverage business, which had $3.2-billion in sales in 2006, the latest available.

What is not clear to everyone is that the alcohol version has cropped up among the non-alcoholic versions.

The state Department of Business and Professional Regulation found in its investigation that some store owners didn't know that some of these drinks contained alcohol, said spokeswoman Alexis Antonacci.

Furthermore, some retail checkouts do not have scanners that automatically warn a cashier when a product contains alcohol.

Green, the Miller Brewing spokesman, said his company does all it can to ensure that their alcoholic beverages are kept out of the hands of minors. He said the company works to educate retailers about displaying and distributing its products.

"No supplier wants their product to get in the hands of under-aged youth," Green said.

But to the critics of Miller Brewing and other alcohol makers, it's as much about the labeling and marketing strategies as what goes on at the retailer.

"We've had teachers who have had students drinking these beverages in class," said Marin Institute's Scippa. "They didn't know it was an alcoholic beverage."

O'Brien, the Wake Forest University researcher, said such actions are needed because the alcohol industry will not own up to its efforts to market to minors.

"Anybody who gets on the Internet can see it's an outright lie," O'Brien. "It really infuriates me that people in the alcohol industry are saying they are not marketing this to youth."

Times staff writer Mariana Minaya contributed to this report. Ivan Penn can be reached at ipenn@sptimes.com or 727-892-2332.

By the numbers:

The so-called alcopops, a combination of alcohol and energy drink, often contain a higher concentration of alcohol by volume than many beers. For example, Sparks has 6 percent alcohol by volume and Tilt has 8 percent, compared with: